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Optical and scanning electron microscopy were used to examine the changes in the surface morphology of optical fibers as a result of acid etching. The resulting surface modifications are modeled and the resulting structures are considered as alternatives to conventional fibers for chemical sensor development. Hydrofluoric acid (HF) etching has been performed on the tips of flat-end graded index fibers, and spherical-end graded and step index fibers. The acid treatment caused the formation of a coneshaped hollow in the center of graded index fiber tips. This structure provides a surface area enhancement of up t o 5.3-fold over untreated fibers. In addition, this cone-shaped cavity provides a sub-nanoliter reservoir in which reagent can be held at the sensing tip of the fiber. Spherical-end fibers provide sur-2123